The present invention relates to a compound sound generator for an information equipment such as a portable telephone.
The compound sound generator has a speaker for converting a call signal into a sound and a receiver for converting a sound signal into a sound. The sound emitted from the receiver is heard with user's ear close to the telephone and the sound emitted from the speaker is heard even when the telephone is away. Thus the speaker generates sounds of larger volume than the receiver.
FIG. 2 is a sectional view of a conventional compound sound generator set in a case 20 of an information equipment.
The compound sound generator has a flat circular or ellipse shape and is set in a case 20 having substantially a shape of a box. In the case 20, there is provided an annular frame 1 made of synthetic resin on which are various parts of the sound generator mounted, and a common yoke 2 made of a magnetic material is mounted in the frame 1.
The yoke 2 comprises a flange 2a formed on an upper periphery of a cylindrical portion 2b having a bottom 2c. An annular first magnet 3 for the speaker is secured to the underside of the flange 2a, and a second magnet 8 for the receiver having disc shape is secured to the bottom 2c of th yoke 2. An annular first top plate 4 made of a magnetic material is secured to the underside of the first magnet 3, and a second top plate 9 having a disc shape is secured to the upper surface of the second magnet 8.
A first diaphragm 6 is secured to the underside of the frame 1, thereby forming a relatively small hack chamber 22a between the diaphragm 6 and the yoke 2. A second diaphragms 11 is secured to the upper surface of the frame 1, thereby forming a relatively small back chamber 22b between the diaphragm 11 and the yoke 2. A first voice coil 5 and a second voice coil 10 are secured to inside surfaces of the first and second diaphragms 6 and 11, respectively. The first diaphragm 6 and the first voice coil 5 compose a first sound production device as a speaker, and the second diaphragm 11 and the second voice coil 10 compose a second sound production device as a receiver. Protectors 7 and 12 each having a dish shape and made of a thin metal plate are secured to the underside and upper surface of the frame 1 for protecting the diaphragms 6 and 11.
There is formed sound discharge holes 7a formed in the protector 7, sound discharge holes 12a in the protector 12.
The outer peripheries of the protector 7 and the diaphragm 6 are inserted and press fitted in an annular recess formed in a lower projection 1a of the frame 1. The outer peripheries of the protector 12 and the diaphragm 11 are inserted and press fitted in an annular recess formed in an upper projection 1b of the frame 1.
The compound sound generator is assembled into the case 20 with other parts. Cushioned annular spacers 21 are disposed between each of the protectors 7 and 12 at outer portions of the sound discharge holes 7a and 12a and the inner space of the case 20.
The case 20 has a plurality of sound discharge holes 20a formed in the bottom thereof and a sound discharge hole 20b formed in the upper surface thereof.
Sound produced by the diaphragm 11 is discharged through the sound discharge holes 12a and further outside through the sound discharge hole 20b as shown by an arrow a. Similarly, sound produced by the diaphragm 6 is discharged through the sound discharge holes 7a and further outside through the sound discharge holes 20a as shown by an arrow b. Mixing of sounds emitted from the back chambers 22a and 22b with the sounds emitted through the sound discharge holes 7a and 12a are prevented. The spacers 21 are provided to enhance the air-tightness, thereby separating the sounds from one another.
In order to allow the vibration of the diaphragms and to improve the acoustic characteristics such as volume and sound quality, the back chambers 22a and 22b are communicated with atmosphere. Namely, as shown by arrows c and d, air in the back chamber 22b flows through openings 1d partially formed in the projection 1b into the inner space of the case 20. Air in the back chamber 22a flows into the inner space of the case 20 through air passages 1c formed in the shoulder of the frame 1 as shown by arrows e and f.
In the conventional compound sound generator, the back chambers 22a and 22b are thus communicated with the entire inner space of the case 20. Therefore, a part of the airflow from one of the back chambers 22b and 22a may flow into the other back chamber through the openings 1d or the passages 1c as shown by arrows g and h. Hence, when the diaphragm 6 for the speaker is vibrated, the produced sound causes the air pressure to change, thereby vibrating the diaphragm 11 for the receiver so that sound is also emitted from the receiver. If a large sound is emitted from the receiver with user's ear close to the telephone, the user's ear may be hurt. In another case, telephone conversation may leak out and be heard by others through the receiver.